Sass has two syntaxes. The new main syntax (as of Sass 3)
is known as "SCSS" (for "Sassy CSS"),
and is a superset of CSS3's syntax.
This means that every valid CSS3 stylesheet is valid SCSS as well.
SCSS files use the extension .scss.

The second, older syntax is known as the indented syntax (or just "Sass").
Inspired by Haml's terseness, it's intended for people
who prefer conciseness over similarity to CSS.
Instead of brackets and semicolons,
it uses the indentation of lines to specify blocks.
Although no longer the primary syntax,
the indented syntax will continue to be supported.
Files in the indented syntax use the extension .sass.

Using

Sass can be used from the command line
or as part of a web framework.
The first step is to install the gem:

gem install sass

After you convert some CSS to Sass, you can run

sass style.scss

to compile it back to CSS.
For more information on these commands, check out

sass --help

To install Sass in Rails 2,
just add config.gem "sass" to config/environment.rb.
In Rails 3, add gem "sass" to your Gemfile instead.
.sass or .scss files should be placed in public/stylesheets/sass,
where they'll be automatically compiled
to corresponding CSS files in public/stylesheets when needed
(the Sass template directory is customizable...
see the Sass reference for details).

Sass can also be used with any Rack-enabled web framework.
To do so, just add

require'sass/plugin/rack'
use Sass::Plugin::Rack

to config.ru.
Then any Sass files in public/stylesheets/sass
will be compiled into CSS files in public/stylesheets on every request.

Formatting

Sass is an extension of CSS
that adds power and elegance to the basic language.
It allows you to use variables, nested rules,
mixins, inline imports,
and more, all with a fully CSS-compatible syntax.
Sass helps keep large stylesheets well-organized,
and get small stylesheets up and running quickly,
particularly with the help of
the Compass style library.

Sass has two syntaxes.
The one presented here, known as "SCSS" (for "Sassy CSS"),
is fully CSS-compatible.
The other (older) syntax, known as the indented syntax or just "Sass",
is whitespace-sensitive and indentation-based.
For more information, see the reference documentation.

To run the following examples and see the CSS they produce,
put them in a file called test.scss and run sass test.scss.

Nesting

Sass avoids repetition by nesting selectors within one another.
The same thing works for properties.

Executables

The Sass gem includes several executables that are useful
for dealing with Sass from the command line.

sass

The sass executable transforms a source Sass file into CSS.
See sass --help for further information and options.

sass-convert

The sass-convert executable converts between CSS, Sass, and SCSS.
When converting from CSS to Sass or SCSS,
nesting is applied where appropriate.
See sass-convert --help for further information and options.

Running locally

To run the Sass executables from a source checkout instead of from rubygems:

Authors

Sass was envisioned by Hampton Catlin
(@hcatlin). However, Hampton doesn't even know his way around the code anymore
and now occasionally consults on the language issues. Hampton lives in San
Francisco, California and works as VP of Technology
at Moovweb.

Natalie Weizenbaum is the primary developer and architect of
Sass. Her hard work has kept the project alive by endlessly answering forum
posts, fixing bugs, refactoring, finding speed improvements, writing
documentation, implementing new features, and getting Hampton coffee (a fitting
task for a girl genius). Natalie lives in Seattle, Washington and works on
Dart application libraries at Google.

Chris Eppstein is a core contributor to
Sass and the creator of Compass, the first Sass-based framework. Chris focuses
on making Sass more powerful, easy to use, and on ways to speed its adoption
through the web development community. Chris lives in San Jose, California with
his wife and daughter. He is an Engineer for
LinkedIn.com, where one of his responsibilities is to
maintain Sass & Compass.

If you use this software, you must pay Hampton a compliment. And buy Natalie
some candy. Maybe pet a kitten. Yeah. Pet that kitty.

Beyond that, the implementation is licensed under the MIT License.
Okay, fine, I guess that means compliments aren't required.